A real-time clock (RTC) is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are almost presented in electronic devices which need to keep accurate time. RTCs normally have an alternate source of power, such as a battery, so they can continue to keep time while the primary source of power is unavailable. The battery life is still limited by the size of the alternative battery. To extend battery life, an RTC system with higher power efficiency is required.